1. Field of the Invention
The present invention relates to an improved recombinant DNA capable being replicated in Escherichia coli in which an improved DNA obtained by substituting with a different amino acid an amino acid located at a specific position in an amino acid sequence of the DNA that codes for glucose dehydrogenase (hereinafter "GDH") originating from Bacillus megaterium has been integrated into an Escherichia coli DNA incorporating vector. It also relates to a transformant containing the same, and a process for preparing a heat-stable GDH by use of the same.
2. Related Background Art
GDH [EC 1.1.1.47] is an important enzyme used as an enzyme for glucose assay system in the field of clinical tests and food industries.
Hitherto known as microorganisms capable of producing GDH are bacteria of the genus Bacillus such as Bacillus megaterium and Bacillus cereus (Japanese Patent Laid-Open No. Sho 53-137199).
However, in order to use GDH as the glucose-quantitating enzyme, a GDH having better stability has been sought to be prepared at a lower cost.
Recently, European Journal of Biochemistry, Vol. 174, pp. 485-490 (1988) has disclosed a method of producing GDH by using a transformant in which GDH gene originating from Bacillus megaterium has been integrated into Escherichia coli.
It teaches that the GDH gene originating from Bascilus megaterium exists in plurality. The transformant is obtained by using them to produce GDH, but the vector used therefor is not suited to the mass production of GDH, and also no improvement has been made at all to more stabilize the GDH.